Solid state matrix for display system or the like



Aug, 12, 1969 L. G. RICH 3,461,344

SOLID STATE MATRIX FOR DISPLAY SYSTEM OR THE LIKE Filed Feb. 16. 1968 2Sheets-Sheet 1 CONDUCTOR RESISTIVE DOTS uenr sm'r'rms 001s TRANSPARENTCONDUCTOR TRIGGERING LOGIC FIG. 3

INVENTOR. LEONARD G. RICH ATTORNEYS 69 L. G. RICH 4 3,461,344

SOLID STATE MATRIX FOR DISPLAY SYSTEM OR THE LIKE Filed Feb. 16, 1968 2Sheets-Sheet 2 i 44" //v 4 4 4 I /7 FlG.6/

FIG. 8

United States Patent 3,461,344 SOLID STATE MATRIX FOR DISPLAY SYSTEM ORTHE LIKE Leonard G. Rich, West Hartford, Conn., assignor to The GerberScientific Instrument Company, South Windsor, Conn., a corporation ofConnecticut Filed Feb. 16, 1968, Ser. No. 706,100 Int. Cl. H!) 37/02,39/08 U.S. Cl. 315-469 16 Claims ABSTRACT OF THE DISCLOSURE A solidstate device consists of a matrix of four layer semiconductor switchelements which may be individually and selectively triggered betweenconducting and nonconducting states and which remain in their lasttriggered state until retriggered or otherwise deliberately returned tothe opposite state. The current passing through the switch elements isused to excite light-emitting elements electrically connected with theswitch elements and distributed in a regular pattern over one face ofthe matrix. Therefore, by properly individually triggering given switchelements to a conducting state a radiant output is produced which may beused as a visible display or as a means for producing photographicallydrawings or other graphic permanent records. As an alternative to aradiant output, the current passing through the switch elements may beused to activate an electro-sensitive paper or the like to produce adrawing or other graphic record on the paper. Also, as a furtheralternative, the device may be designed to operate in a flash mannerwherein each stack, when triggered to a conducting state, thereafterquickly reverts to its non-conducting state so that the output elementactivated by the current through the switch element is excited for onlya short predetermined interval of time.

Background of invention This invention relates to display systems or thelike wherein a visible display or drawing is made by selectivelyexciting discrete minute portions of a display or output surface, and itdeals more particularly with the construction of a solid state matrixdevice which provides such an output surface, the matrix being dividedinto a large number of individual units each exclusively associated witha particular minute portion of the surface and connected so as to bereadily selectively addressable by triggering or other control signals.

Summary of invention The solid state matrix device of this inventionincludes a display or output surface divided into a very large number ofminute discrete portions or dots arranged in a regular pattern over thesurface. Each of these dots may be a small light-emitting element which,when excited by an electric current, emits radiant light energy, or maymerely constitute an electrode for passing an electric current throughan electro-sensitive paper or the like placed against the outputsurface. Associated with each discrete portion or dot of the displaysurface is a semiconductor switch element which functions generallysimilarly to a silicon controlled rectifier and which may be triggeredbetween conducting and non-conducting states to. permit or preventelectric current from a suitable source to pass through the switchelement to the associated dot of the output surface. The device may bemade by well-known integrated circuit techniques and preferablyconstitutes a number of layers of different material superimposed on oneanother with the material of each layer divided into separate dots orother shapes and properly arranged and ice registered with the materialof the other layers as to form individual stack-like units arranged in aregular pattern of rows and columns. The basic part of each stack-likeunit of the matrix device is the switch element which is comprised offour alternately doped layers of semiconductive material. The secondlayer of all of the switch elements associated with one row ofstack-like units are electrically connected in common. Similarly, thethird layers of all of the switch elements in each column of stack-likeunits are connected in common, with the result that any one particularswitch element may be triggered to a conducting state by simultaneouslyapplying triggering signals to the column and row terminals whichintersect at said switch element. Therefore, by combining the matrixdevice of this invention with a computer or other logic device whichprovides a system of sequencing the control of the triggering signaldrive on the columns and rows is possible to produce a continuouslyvariable controllable display system.

Brief description of the drawing FIG. 1 is an enlarged, exploded, andsomewhat schematic view of a solid state matrix device embodying thisinvention.

FIG. 2 is an enlarged, somewhat schematic view of the solid state matrixdevice of FIG. 1 as incorporated in a display system.

FIG. 3 is a schematic diagram illustrating the equivalent electricalcircuit for two of the stack-like units in the matrix device of FIG. 1.

FIG. 4 is a still greater enlarged view showing schematically thedifferent layers making up one of the stack-like units of the matrixdevice of FIG. 1.

FIG. 5 is a view generally similar to FIG. 4 but shows a one stack-likeunit of a matrix device comprising an alternate embodiment of theinvention.

FIG. 6 is a view generally similar to FIG. 4 but shows one stack-likeunit of a matrix device comprising still another embodiment of theinvention.

FIG. 7 is a view generally similar to FIG. 4 but shows two stack-likeunits of a matrix device comprising still another embodiment of theinvention.

FIG. 8 is a view taken on the line 88 of FIG. 7.

Description of the preferred embodiments Turning now to the drawings,FIGS. 1 and 2 show in greatly enlarged form a solid state matrix device10 embodying this invention. The illustrated device 10 may be taken assubstantially complete, but normally an actual device would consist of avery much larger number of stack-like units. Also, in FIGS. 1 and 2various terminals required for making electrical connection with variousparts of the device 10 have been eliminated for clarity. Such terminalsmay be added to the device in any well known manner and by themselvesform no essential part of the invention. As is obvious from FIGS. 1 and2 the device 10 is formed of a number of different layers of materialsuperimposed on one another, and in FIG. 1 the device is shown in anexploded form with the various different layers separated from oneanother.

Considering FIGS. 1 and 2 in more detail, the device 10 there shownincludes four layers 12, 13, 14 and 15 of semiconductor material whichtogether'form the basic switch elements of the various stack-like units.The bottom layer 12 consists of a large number of small discrete areasor deposits 16, 16 of semiconductive material. In the illustrated casethe areas 16, 16 are shown to be generally square in shape, and forconvenience these small areas or deposits of material, and similar areasor deposits of material in other parts of the device, will be referredto hereinafter as dots. These dots, however,

. 3 need not be square in shape andmay be circular or any other suitableshape, the term dot being intended to apply to any such shape. In thelayer 12, the dots 16, 16 are arranged in a regular pattern to form fiverows of dots extending generally parallel to the arrow 17 and sixcolumns of dots extending generally parallel to the arrow 18. In theareas not covered by the dots 16, 16 the layer 12 includes a suitableelectrical insulating material 20 which electrically isolates the dotsfrom one another.

The layer 13 immediately above the bottom layer 12 consists of a numberof strips 22, 22 of semicond'uctive material which extend generallyparallel to the rows of dots 16, 16 in the bottom layer 12 and each ofwhich directly overlies a respective one of said rows. The layer 14immediately above the layer 13 consists of a number of strips 24, 24 ofsemiconductive material, each extending along and located directly abovea respectiveone of the columns of the dots 16, 16 of the layer 12. Thetop layer 15 consists of a number of dots 26, 26 of semiconductivematerial arranged in the same pattern as the dots 16, 16 of the layer 12and each located directly above a respective one of the dots 16, 16. Thespaces between the strips 22, 22 of the layer 13, the strips 24, 24 ofthe layer 14 and the dots 26, 26 of the layer 15 are filled with theelectrical insulating material 20.

-The four semiconductive layers 12, 13, 14 and 15 may be formed inaccordance with various different well known methods for formingmulti-layered integrated circuit devices, as for example by forming eachlayer epitaxially through the use of suitable masks. The semiconductivematerials used in the four layers are alternately doped withapproximately the same concentrations of impurities as used in thecorresponding layers of a silicon controlled rectifier. As shown in FIG.1 the dots 2 6, 26 of the layer 15 are of -p-type conductivity material,the strips 24, 24 of the layer 14 are of n-type conductivity material,the strips 22, 22 of the layer 13 of p-type conductivity material andthe dots 16, 16 of the layer 12 are of n-type conductivity material. Itwill therefore be evident that in the device 10, a large number of PNPNsemi-conductor switch elements are provided with each being comprised ofone dot 16 of the bottom layer 12, one strip 22 of the next layer 13,one strip 24 of the layer 14 and one dot 26 of the top layer 15. Itshould be understood, however, that although a PNPN configuration hasbeen shown for these switch elements they could as well be made of anNPNP configuration without departing from the invention.

In addition to the four semiconductive layers 12,13, 14 and 15 whichform the basic switch units, the device 10 of FIGS. 1 and 2 furtherincludes a light-emitting layer 28 made up of a large number of elementsor dots 30, 30 arranged in the same pattern as the dots 16, 16 of thelayer 12 and each registered with a respective one of the (lots 16, 16.Each dot 30 is of such a nature as to emit light radiation when excitedby an electric currentpassing therethrough from the associated dot 16.Various different materials may be used to form the dots 30, 30, butpreferably each dot 30 is a small light-emitting diode, and when this isthe case each element 30 may 'either be a two layer diode by itself ormay be a single layer of material with the material of the associateddot 16 forming the other part of the diode. Insulating material 20 fillsspaces between the individual dots 30, 30 to electrically isolate themfrom one another.

.Below the light-emitting layer 28 is a layer 32 of transparentconductive material which allows the radiation emitted by the lightemitting dots 30, 30 to pass therethrough and which serves as a commonterminal elec- -the light emitted by the dots 30, 30 is in the visiblerange. This picture or graphic display may be viewed directly by a useror may be used to expose a photosensitive sheet placed over the bottomsurface to photographically produce a permanent record of the display.

As a means for supplying exciting current to each of the switch elementsof the device 10, the device further includes two additional layersabove the top semiconductive layer "15. The layer 36 immediately abovethe layer 15 is referred to as an ohmic layer and consists of a largenumber of dots 38, 38 of ohmic material, which dots 38, 38 are arrangedin the same pattern as the dots 26, 26 of the layer 15 with eachregistered with a re spective one of the latter d'ots. Above the layer36 is a final layer 40 consisting of a sheet of conductive .materialwhich electrically connects all of the top surfaces of the ohmic orresistive dots 38, 38. If desired, the ohmic dots 38, 38 may be formedby forming a coating of ohmic material on the conductive sheet formingthe layer 40, prior to its assembly with the remainder of the device 10,and by then scribing the ohmic layer to divide it into the dots 38, 38.

FIG. 4 shows a vertical section taken through one stack-like unit 42 ofthe device of FIG. 1, and FIG. 3 shows a general electrical equivalentor transistor analog of two adjacent units 42, 42. In FIG. 3 the variousparts of the equivalent circuit have been given the same referencenumbers as the elements of the device 10 to which they are generallyequivalent. From these figures it will therefore be evident that in eachunit the two dots 16 and 26 and two strips 22 and 24 of semiconductivematerial form a triggered switch, generally similar to a siliconcontrolled rectifier. Also, from FIG. 3 it will be evident that byproper biasing each such triggered switch may be made to operate in sucha fashion that a negative triggering signal must be applied to strip 24simultaneously with a positive triggering signal applied to the strip 22in order to switch it from a non-conducting to a conducting state, andthat once it is rendered conducting it will remain in such conductingstate until turned off by a further turn off procedure as, for example,simultaneously applying reverse triggering pulses to the strip 24 andthe strip 22 or momentarily turning off all points to momentarily reduceall currents through the device 10 to zero.

As shown in FIGS. 2 and 4, the upper and lower conductive layers 32 and40 of the device 10 are connected to a suitable voltage source 44 sothat when a particular element 42 is switched to a conducting statecurrent flows therethrough from the source 44 to excite the associatedlight-emitting element 30. The ohmic element 38 of each stack-like unit42 serves as a current limiting device and in some cases may beeliminated. FIG. 2 shows a typical application of the device 10 whereinall of the strips 24, 24 of the layer 14 and all of the strips 22, 22 ofthe layer 13 are connected to a triggering logic 46 which may, forexample, be part of a computer. Because of the strips 22, 22 extendingin one direction and the strips 24, 24 extending in another direction,each stack-like unit in the device 10 is selectively addressable bytriggering signals applied simultaneously to the strip 22 and the strip24 which intersect and are exclusively paired in that particular unit.Therefore, the triggering logic 46 by properly sequencing triggeringsignals to the strips 24, 24 and 22, 22 may be used to excite thoselight-emitting elements required to produce a desired display on theoutput surface 34 of the device 10. Of course, as mentioned previously,the number of stack-like units in the device 10 may be increased verygreatly beyond the number shown in FIGS. 1 and 2 to produce a relativelylarge output surface divided into very small discrete dots. It shouldalso be understood that by proper selection of the material used forproviding the light-emitting dots, the device 10 is capable of producingcolor. The device 10 could therefore be designed for use in a systemcapable of providing both monocrome and color displays and pictures.Also, the triggering logic 46, could be such as to rapidly andrepeatedly change the picture or display produced at the output surface34 to produce a moving picture as in television, the device therebybecoming the equivalent of a fiat television tube.

FIG. 5 is a section taken through one stack-like unit of a matrixdevice, indicated generally at 48, which is generally similar to thedevice 10 of FIGS. 1 to 4, except for omission of the light-emittinglayer 28and the transparent conductive layer 32 of the device 10. Partsof the device 48 which are similar to corresponding parts of device 10have been given corresponding reference numbers and need not be furtherredescribed. In the device 48, the output surface 50 is located at thebottom of the semiconductive layer 12 with the lower face of eachsemiconductive dot 16 forming a small part of said output surface. Inuse the device 48 has its upper conductive surface connected to thepositive side of a suitable voltage source 52, and the negative side ofthe source 52 is connected to a conductive bed or plate 54. Anelectrosensitive paper 56 or the like is placed between the outputsurface 50 and the upper surface of the bed 46 so that each dot 16 ofthe device 48 contacts a small discrete area of the paper 56. Therefore,when the switch element of which the illustrated dot 16 is a part istriggered to its conducting state current flows through theelectro-sensitive paper 56, from the dot 16 to the bed 54, andelectrically activates the paper over the area covered by the dot.Therefore, if the paper 16 is one which changes color or tone as aresult of electrical activation, a picture or other graphic display maybe made on it by properly triggering selected ones of the switchelements making up the device 48.

As an alternative to a matrix device wherein the individual switchelements remain in a conducting state until deliverately turned to anon-conducting state, a matrix device embodying this invention may alsobe made for use in a flash mode of operation wherein each switch elementonce triggered to its conducting state remains in such conducting statefor a predetermined length of time and is then automatically returned toits non-conducting state. To achieve this kind of operation the matrixdevice is constructed so as to include a plurality of capacitors eachassociated with a respective one of the switch elements.

FIG. 6 shows a matrix device 58 incorporating one form of capacitor.Parts of the device 58 which are similar to corresponding parts of thedevice 10 of FIGS. 1 to 4 have been given the same reference numbers asin FIGS. 1 and 4 and need not be re-described. The device 58 isidentical to that of the device 10 except for including in eachstacklike unit a dot of material 60 replacing the ohmic dot 38 ofFIG. 1. The material of the dot 60 is one, such as barium titanate,having a high dielectric constant and a slight electrical conductivityso as to form a leaky capacitor between the semiconductive dot 26 andthe conductive layer 40. In the use of the device 58, when simultaneoustriggering signals are applied to the strip 22 and the strip 24 of aparticular switch element, the switch element conducts to excite itsassociated light-emitting dot 30 and to charge the capacitor formed bythe associated dielectric dot 60. As this capacitor becomes charged thecurrent through the switch element device falls below the conductionsustaining level and the switch thereupon reverts to its non-conductingstate, the capacitor thereupon discharging through the material of thedot 60 to make itself ready for another cycle of operation.

FIGS. 7 and 8 show a section through two adjacent stack-like units of amatrix device 62 in which a capacitor for each unit is formed byreplacing the ohmic layer 36 of the device 10 of FIGS. 1 to 4 with aconductive layer 64 and a dielectric layer 66. The conductive layer, asbest shown in FIG. 8, includes a number of dots 68, 68 of conductivematerial arranged in the same pattern as the dots 26, 26 of the layerand registered with the dots 26, 26. Surrounding each of the conductivedots 68 is a region of ohmic material 70, and in the otherwise emptyspace beyond the outer edge of the regions 70, is a common conductivematerial 72. As a result, each conductive dot 68 is connected to thecommon conductor 72 through a resistance provided by the associatedohmic material 70. The dielectric layer 66, in turn, includes a numberof dots of dielectric material 74, 74 arranged in the same pattern asthe dots of conductive material 68, 68 and registering with the latterdots, the spaces between the dots 74, 74 being filled with electricinsulating material 20 so as to electrically isolate the dielectric dots74, 74 from one another.

In the use of the device 62 of FIGS. 7 and 8, the common conductor 72 ofthe conductive layer 64 is connected to one side of a suitable voltagesource 76 and the other side of the source is connected to thetransparent conductive layer 32. The transparent conductive layer 32 isalso grounded as is the upper conductive layer 40. Therefore, when aparticular stack-like unit of the device 62 is in its non-conductingstate the associated capacitor, formed by the dielectric dot 74, theconductive dot 68 and conductive layer 62, is charged. When simultaneoustriggering signals are applied to the strips 22 and 24 of thisparticular stack-like unit, the unit is rendered conductive and conductsthrough it the charge of its associated cacapitor, this conduction beingmaintained until the capacitor becomes discharged to the point where thecurrent falls below the conduction sustaining level. Thereafter, thedevice reverts to its non-conducting state and the capacitor rechargesfor a new operating cycle.

The drawings show preferred embodiments of the invention and suchembodiments have been described above, but it will be understood thatvarious changes may be made from the constructions disclosed, and thatthe drawings and description are not to be construed as defining orlimiting the scope of the invention, the following claims forming a partof this specification being relied upon for that purpose.

I claim:

1. A solid state matrix device comprised, at least in part, of fourlayers of semiconductive material superimposed on one another andforming a plurality of switch elements which may be selectivelytriggered between conducting and non-conducting states, the bottom oneof said layers consisting of a plurality of individual dots ofsemiconductive material of one type conductivity arranged regularly in anumber of columns extending in one direction and a number of rowsextending in another direction, the layer immediately above said bottomlayer consisting of a plurality of individual strips of semiconductivematerial of opposite type conductivity arranged so as to extend alongand overlie said rows of said dots in said bottom layer, the layerimmediately above said layer of row-wise oriented strips consisting of aplurality of individual strips of semiconductive material of said onetype conductivity which latter strips are arranged so as to extend alongand overlie said columns of said dots in said bottom layer, and the topone of said layers consisting of a plurality of individual dots ofsemiconductive material of said opposite type conductivity arranged inthe same pattern as the dots of said bottom layer so that each overliesa respective one of said latter dots.

2. A solid state matrix device as defined in claim 1 furthercharacterized by a layer of ohmic material immediately above said toplayer of said four layers of semiconductive material, said ohmic layerconsisting of a plurality of individual dots of ohmic material arrangedin the same pattern as the dots of said top layer so that each overliesa respective one of said latter dots.

3. A solid state matrix device as defined in claim 2 furthercharacterized by a layer of conductive material located immediatelyabove said ohmic layer and electrically connecting the top surfaces ofall of said dots of ohmic material.

4. A solid state matrix device as defined in claim 1 furthercharacterized by a light-emitting layer of material located immediatelybelow said bottom layer of said four layers of semiconductive material,said lightemitting layer consisting of a plurality of individualelements arranged in the same pattern as said dots of said bottom layerso that each overlies a respective one of said latter dots, each of saidelements of said lightemitting layer being of such nature as to emitlight radiation when an electric current passes between it and saidrespectively associated one of said dots of said bottom layer.

5. A solid state matrix device as defined in claim 4 furthercharacterized by each of said elements of said light-emitting layercomprising a quantity of semiconductive material forming alight-emitting diode in conjunction with said respectively associateddot of said bottom layer.

6. A solid state matrix device as defined in claim 4 furthercharacterized by a layer of transparent conductive material locatedbelow said light-emitting layer.

7. A solid state matrix device as defined in claim 1 furthercharacterized by means forming a plurality of capacitors above said toplayer of said four layers of semiconductive material with each of saidcapacitors having one terminal electrically connected with a respectiveone of said dots of said top layer and having its other terminalconnected in common to the corresponding terminals of the other of saidcapacitors.

8. A solid state matrix device as defined in claim 7 furthercharacterized by said means forming a plurality of capacitors comprisinga dielectric layer located immediately above said top layer of said fourlayers of semiconductive material and consisting of a plurality of dotsof material of high dielectric constant arranged in a pattern similar tothat of said dots of said top layer so each overlies a respective one ofsaid latter dots, and a layer of conductive material above saiddielectric layer electrically connecting the top surfaces of all of saiddots of dielectric material.

9. A solid state matrix device as defined in claim 7 furthercharacterized by said means forming a plurality of capacitors comprisinga first terminal layer immediately overlying said top layer of said fourlayers of semiconductive material, a dielectric layer overlying saidfirst terminal layer, said first terminal layer comprising a pluralityof conductive dots arranged in the same pattern as said dots of said toplayer of said four layers of semiconductive material and arranged sothat each engages the top surface of a respective one of said latterdots, said first terminal layer further including a common conductorspaced from each of said conductive dots and an ohmic material betweeneach of said conductive dots and said common conductor, said dielectriclayer comprising a plurality of dots of material of high dielectricconstant arranged in a pattern similar to that of said conductive dotsand arranged so that each overlies a respective one of said latter dots,and a layer of conductive material above said dielectric layerelectrically connecting the top surfaces of all of said dots ofdielectric material.

10. A solid state matrix device as defined in claim 1 furthercharacterized by a layer of ohmic material immediately above said toplayer of said four layers of semiconductive material, said ohmic layerconsisting of a plurality of individual dots of ohmic material arrangedin the same pattern as said dots of said top layer so that each overliesa respective one of said latter dot-s, a layer of conductive materiallocated immediately above said ohmic layer so as to electrically connectthe top surfaces of all of said dots of ohmic material, a light-emittinglayer of material located immediately below said bottom layer of saidfour layers of semiconductive material, said light-emitting layerconsisting of a plurality of individual elements arranged in the samepattern as said dots of said bottom layer so that each underlies arespective one of said latter dots, each of said elements of said lightemitting layer being of such nature as to emit light radiation when anelectric current passes between it and said respectively associated oneof said dots of said bottom layer and a layer of transparent conductivematerial located below said light-emitting layer.

11. A solid state matrix device having an output surface divided into alarge number of discrete dots arranged regularly in a number of columnsextending in one direction and a number of rows extending in anotherdirection, said matrix device including a plurality of semiconductorswitch devices each exclusively electrically connected with a respectiveone of said dots and each consisting of four alternately doped layers ofsemiconductive material, the second and third of said four layers beinglocated between the first and fourth of said four layers, meanselectrically connecting in common the second layers of said switchdevices associated with each of said rows of dots, and meanselectrically connecting in common the third layers of said switchdevices associated with each of said columns of dots.

12. A solid state matrix device as defined in claim 11 furthercharacterized by each of said dots being defined by one surface of alight-emitting element electrically connected with a respective one ofsaid semiconductor switch devices and of such nature as to emit lightradiation when an electric current passes'through it from saidassociated semiconductor switch device.

13. A solid state matrix device as defined in claim 11 furthercharacterized by each of said dots being defined by one surface of saidfirst and second layers of its associated semiconductor switch device.

14. A solid state matrix device having an output surface divided into alarge number of discrete dots arranged regularly in a number of columnsextending in one direction and a number of rows extending in anotherdirection, said matrix device including a plurality of semiconductorswitch devices each exclusively electrically connected with a respectiveone of said dots and each including first and second layers ofsemiconductive material to which simultaneous triggering signals need beapplied to switch it from a non-conducting to a conducting state, meanselectrically connecting in common the said first layers of said switchdevices associated with each of said rows of dots, and meanselectrically connecting in common the said second layers of said switchdevices associated with each of said columns of dots.

15. A solid state matrix device as defined in claim 14 furthercharacterized by each of said dots being defined by one surface of alight-emitting element electrically connected with a respective one ofsaid semiconductor switch devices and of such nature as to emit lightradiation when an electric current passes through it from saidassociated semiconductor switch device.

16. A solid state matrix device as defined in claim 14 furthercharacterized by each of said dots being defined 'by one surface of saidfirst and second layers of its associated semiconductor switch device.

-' References Cited UNITED STATES PATENTS 3,214,595 10/1965 Johnson etal 2502l9 3,258,644 6/1966 Rajchman 31555 3,375,373 3/1968 Hageman250-209 3,388,255 6/1968 May 250-209 JOHN W. HUCKERT, Primary ExaminerS. BRODER, Assistant Examiner U.S. Cl. X.R.

